The generation of superoxide radicals in biological systems, the chemical bases of the deleterious actions of that radical and the importance of superoxide dismutases as defenses against these deleterious actions shall continue to occupy our attention. Among the specific projects which fall under this purvue and which shall be actively pursued are the following: a. Isolate mutants of E. coli defective with respect to the mangani or the ferri superoxide dismutases and compare these with the wild type with respect to susceptibility to oxygen toxicity, phagocytic kill, radiation lethality, streptonigrin toxicity and paraquat toxicity. b. Demonstrate mutagenicity of hyperbaric oxygen towards E. coli and see whether high levels of superoxide dismutase protect against this mutagenicity. Are mutants defective in superoxide dismutase, catalase or peroxidase extra sensitive towards oxygen mutagenicity? c. Measure the rate constants of the Haber-Weiss reaction as a function of pH and of temperature. Demonstrate occurrence of Haber-Weiss reaction - in vivo. d. Attempt reversible removal of metal prosthetic groups from E. coli ferri and mangani superoxide dismutases. Attempt to replace natural prosthetic groups by other metals.